Since you have set up your own domain and miiduu.com will never display in your store URL any longer, you cannot use Miiduu's shared SSL certificate. This means you have to get a new SSL certificate for your own domain.
To do this, please go to Settings-> Own domain, Select "Yes" for Use Own SSL option and click "save", you will be shown the SSL plan ($99 one time payment). You can click "Sign up now" to pay the SSL certificate via PayPal. After the payment goes through, we will set up the SSL certification for your own domain. You can have the SSL certificate as long as your miiduu account is active.